Temperature responsive control



States Patent i R'obertshawFulton Controls Company, Greensburg,

Pa., a corporation of Delaware Original pplication September 8, 1954,Serial No. 454,753. Divided and this application December 14, 1956,Serial Nd. 628,371

7" claims. Cl. 200-140 This application is a division of our applicationSerial No. 454,753, filed September 8, 1954. This invention relates tothermostat control devices and more particularly to an improved devicewhich is particularly adapted for controlling the surface heatingelement of an electric range.

Many foods require rapid initial heating to bring the food to apredetermined temperature and thereafter require a reduced amount ofheat input to maintain such predetermined temperature. It is an objectof this invention to effect such a cooking operation by permitting theheating element to operate at full energy input until the temperature ofthe food to be cooked reaches a predeterminedvalue, and then reducingenergy input to the heating element to maintain the food at the propertemperature.

Another object of this invention is to incorporate in a thermostaticcontrol device a switching mechanism for reducing energy input to aheating element as the control temperature is approached during anincrease in temperature.

Another object of this invention is to reduce the rate of energy inputto a heating element by a switching mechanism operative in one positionto connect the heating element across a source of reduced voltage.

In the preferred embodiment of the invention, a switch arm is pivotallymounted in a casing and extends between a pair ofrelatively fixedcontacts. The switch arm carries a pair of oppositely disposed contactswhich are engag'ea'ble with the fixed contacts respectively. One of therelatively fixed contacts is mounted on one end (if the second switcharm which carries an adjustable stop adj'a'cent its other end and ispivoted intermediate its ends on the casing. Thermally responsive meansare provided including an expansible element mounted on said casing anden'ga'gc'able' with the first said switch ar'm. Upon an increase intemperature, the first switch arm will move one of its contacts out ofengagement with one of the fixed contacts and move the other of itscontacts into engagement with a relativelyfixed contact to connect thesurface heating element to a source of reduced power. Upon furtherincrease in temperature, an abutment carried by the first switch armengages the second switch arm to disengage their associated contacts andterminate the supply or power to the heating'eler'nent.

Other objects and advantages will become apparent from the followingdescription taken in connection with the accompanying drawings wherein:

Fig. l is a schematic view of the control device embodying thisinvention and a surface heater for an electricrange; and i H Fig. 2 is avi'ewsiinilar t'o'Fig. 1 but showing a modified form ofinven'tion.

Referring more particularly to Fig. 1, there is shown an annmar surfaceheating element 10 which is adapted to'besupported on the top plate ofan electric range (not shown) in a manner well known inthe art. Theheating element 10' is adapted to support a cooking vessel 12- PatentedMay 6, 1958 thereon and is provided with a temperature sensing Bulb 14which is located centrally thereof.

The bulb 14 takes the form of a flat, hollow container whichcommunicates with a capillary tube 16 and is biased toward the cookingvessel 12 by a spring 18 seated an; suitable stirrup 20. The particularstructure of the bulb 14 and mounting therefor is fully disclosed andclaimed in our co-pending application Serial No. 454,754, filedSeptember 8, 1954, which'is now Patent No. 2,7 86,930.

The capillary tube 16 also communicates with an expansible power element22 which may consist of a pair of flexible diaphragms welded together attheir periphery and carrying a thrust button 24 on one side thereof. Theother side of the power element 22 is secured to a stiid 26 which isthreaded through a suitable aperture 28 formed in the wall of the casing30 to mount e power element 22 in a chamber 32 formed in the casing 30.

One end of the stud 26 projects from the casing 30 and carries amanually operable knob or dial 34 which may be manipulated to rotate thestud 26 and thus etfect axial adjustment of the power element 22relative to the casing 30.

The assembly of the bulb 14, capillary tube 16, and expansible powerelement 22 is filled with a suitable thermal fluid which will expandupon increase in temperature sensed by the bulb 14 to effect expansionof the power elethem 22. p

A switch arm' 36 is pivotally mounted in the casing 30 and is connectedat one end to a lead wire 38 which in turn is connected to the surfaceheater 10. The switch arm 36 underlies the expansible power element 22and carries a block of insulating material 40 which is biased intoengagement with the thrust button 24 by a suitable spring 42 acting onthe switch arm 36. The other end of the switch arm 36 extends between apair of contacts 46, 48 and carries a pair of oppositely disposedcontacts 50', 52 engageable with the contacts 46, 48, respectively.

The contact 48 is mounted on one end of a second switch arm 54 whichcarries an adjustable stop in the form of a screw 56 adjacent its otherend and is pivoted intermediate its ends on the casing 30 by means of alug 58 and pin 60. A spring 62' acts between the switch arm 54 and thecasing 30 to normally hold the screw 56 seated on the casing 30 andthereby position the contact 4'8 in predetermined spaced relation withthe contact 52. The switch arm 36 extends beyond the contacts 46, 48 andcontacts 50, 52 and carries a projection 64 on its extrernity whichoverlies the switch arm 54.

The contact 46 is connected to one line wire L1 of a suitable three-wiresource of electric power and the switch arm'54 is connected to a neutralwire N. T 0 provide for an off position of the dial 34, this member isprovided with suitable cammeans 66 which co-act with the normally closedswitch- 68 to open the same in a selectedposition of the dial 134. Afixed contact 70 of the switch means 68 is connected to the line wire L2of the source, and a movable contact 72 is connected to the heatingelement 10 by a lead wire 74.

As shown, the apparatus'of Fig. l is in the otf position with noelectrical energy being supplied to the surface heating element 1t Toplace the apparatus in operation, the dial 34 is rotated to a desiredtemperature setting.. Such rotation of the dial 34 will move the cammeans 66 out of engagement with the switch 68 and permit the latter toclose. The temperature setting movement of the dial 34 will also serveto screw the stud 26 out of the casing 30 and move the power element 22upward, thereby permitting the switch arm 36 to pivot under the bias'ofthe spring and move the contact 5t} into engagement withthe fixedcontact 46.

The apparatus is thus conditioned to supply relatively large amounts ofelectric energy to the surface heating element to a circuit which may betraced as follows: line wire L2 of the three-wire power source, switch68, wire 74, heating element 10, wire 38, switch arm 36, and contacts50, 46 and line wire L1. Thus, the surface heating element 10 isconnected directly across line wires L1, L2 which may have a potentialdifference on the order of 230 volts. Accordingly, heat will begenerated by the surface heating element 10 at a relatively rapid rateto raise the temperature of the cooking vessel 12 and the food containedtherein.

As the temperature of the cooking vessel 12 rises, the temperature ofthe bulb 14 will increase to cause expansion of the power element 22.Expansion of the power element 22 will move the thrust button 24 intoengagement with the switch arm 36 to swing the same against the bias ofthe spring 42, thereby moving the contact 50 out of engagement with thefixed contact 46 and moving the contact 52 into engagement with thecontact 48 after having opened contacts 46, 50.

At this point, the surface heating element 10 is energized through acircuit which may be traced as follows: line wire L2, switch 68, wire74, heating element 10, wire 38, switch arm 36, contacts 48, 52, switcharm 54 and neutral wire N of the power source. Thus, the heating element18 is connected directly across line wire L1 and neutral wire N whichmay have a potential difference on the order of 115 volts. When theapparatus is in this condition, the rate of energy input to the heatingelement 10 is substantially less than when the same is connecteddirectly across line wires L1, L2. Thus, the heat produced by theheating element 10 and transmitted to the cooking vessel 12 is alsosubstantially less. Heat supplied to the cooking vessel 12 at thisreduced rate continues to raise the temperature of the contents thereofgradually to the desired temperature.

As the temperature of the vessel 12 rises as a result of the reducedenergy input due to the heating element 10, such temperature rise issensed by the bulb 14, and consequently, the power element 22 continuesto expand. The continued expansion of the power element 22 moves theprojection 64 on the switch arm 36 into engagement with the switch arm54, causing the latter to be pivoted in a counterclockwise direction tomove the contact 48 out of engagement with the contact 52. Separation ofthe contacts 48, 52 will break the last traced energizing circuit forthe surface heating element 16 and the supply of heat to the vessel 12will be terminated.

As the temperature of the vessel 12, as sensed by the bulb 14, drops,the power element 22 will contract to permit the switch arm 36 to movein a counterclockwise direction under the bias of the spring 42. Suchmovement of the switch arm 36 will raise the projection 64 and permitclockwise movement of the switch arm 54 under the bias of the spring 62to bring the contact 48 into engagement with the contact 52 and onceagain complete the circuit for energizing the heating element 10 at arelatively low input rate.

Usually, restoration of the reduced rate of heat input serves to restorethe desired temperature to the vessel 12 to again cause expansion of thepower element and opening or" the contacts 48, 52. However, in the eventthat the reduced input rate is not sufiicient to restore the desiredtemperature, the power element 22 may contract sufiiciently to open thecontacts 48, 52 and subsequently close the contacts 46, 50 therebycompleting the circuit which provides a relatively high input rate tothe heating element 10.

It will be apparent from the foregoing that the apparatus shown in Fig.l is operative to bring the temperature of the cooking vessel rapidly upto a temperature approaching the desired control temperature thusapplying power at a relatively high rate to the heating element 10 andthereafter effecting a gradual temperature rise in the cooking vessel 12to the selected cooking temperature by 4 supplying power at a reducedrate to the heating element 10. Subsequent maintenance of the selectedtemperature of the cooking vessel 12 is effected by supplying power at ahigh or low rate to the heating element 10 in response to temperaturevariations of the cooking vessel 12.

The temperature at which the power supplied to the heating element 10 isswitched from a high to a low rate is accurately determined by thesetting of the dial 34. It will be apparent that the screw 56 carried bythe switch arm 54 may be adjusted to position the contact 48 forengagement with the contact 52 after separation of the contacts 46, 58.

The embodiment of the invention shown in Fig. 2, wherein partscorresponding to parts hereinbefore described are given like referencenumerals, is similar to the embodiment shown in Fig. l but differstherefrom in the form of the switching mechanism for terminating thesupply of electric energy to the surface heater 10.

The switch arm 54 of Fig. 2 carries a contact 48 on one end thereof forengagement with the contact 52 but carries a second contact 76 on theother end thereof in place of the adjusting screw 56 shown in Fig. 1.The contact 76 is movable with the switch arm 54 and is engageable witha fixed contact 78 which is connected to the neutral wire N of thethree-wire power source.

The contact 46 which is engageable with the contact 50 on the switch arm36 is carried on a lever 80. The lever 80 is pivotally mounted on thecasing 30 by means of a pin 82 and is biased into engagement with anadjusting screw 84 by a spring 86. It will be apparent that theadjusting screw 84 controls the position of the contact 46 relative tothe casing 30 and thus may be manipulated to effect proper positioningof the contact 46 relative to the contact 50. This arrangement insuresthat the contact 52 will not engage the contact 48 until after thecontacts 46, 50 have been separated.

Operation of the apparatus shown in Fig. 2 is similar to the operationof that shown in Fig. 1, dilfering only in that the energizing circuitwhich supplies energy to the heating element 10 at a relatively lowrate, is broken by separation of the contacts 76, 78 rather than byseparation of the contacts 48, 52. The contacts 48, 52 are normally heldin engagement with each other by the bias of the spring 62 and are movedout of engagement with each other upon excessive expansion of the powerelement 22 in response to a temperature of the cooking vessel 12 whichis higher than the selected control temperature.

While only two embodiments of the invention have een herein shown anddescribed, it will be obvious to those skilled in the art that theinvention may be variously embodied and that changes may be made in theconstruction and arrangement of parts without departing from the scopeof the invention as defined in the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A thermostatic control device comprising, a casing, first switchmeans in said casing having open and closed positions for controlling afirst circuit, second switch means in said casing having open and closedpositions for controlling a second circuit, means responsive to atemperature condition including a member mounted on said casing andmovable in response to a change in the temperature condition, meansoperatively connected to said member-and said first and second switchmeans for maintaining said first switch means in said closed positionand said second switch means in said open position in response to saidtemperature condition and for sequentially actuating said first switchmeans from said closed position to said open position and said secondswitch means from said open position to said closed position in responseto an increase in the temperature condition, and means operativelyassociated with said member and said second switch means for actuatingsaid second switch means to said open position in response to a fultherincrease in the temperature condition.

2. In a thermostatic control device, the combination comprising acasing, first switch means in said casing having open and closedpositions for controlling a first circuit, second switch means in saidcasing having open and closed positions for controlling a secondcircuit, a pivotal lever operatively associated with said first andsecond switch means for actuating the same between said positions, meansresponsive to a temperature condition including a movable elementoperatively connected to said lever for sequentially actuating saidfirst switch means from said closed position to said open position andsaid second switch means from said open position to said closed positionin response to an increase in the temperature condition, and meansincluding said lever for actuating said second switch means to said openposition in response to a further increase in the temperature condition.i

3. In a thermostatic control device, the combination comprising acasing, a fixed contact mounted within said casing, a fixed pivotallever mounted in said casing, 21 second contact mounted on one end ofsaid lever in spaced relation to said fixed contact, a second pivotallever mounted in said casing and having contact means thereon formovement into and out of engagement with said fixed and second contacts,means responsive to a temperature condition including an expansible andcontractible element mounted on said casing and being engageable with.said lever for actuating said second contact means out of engagementwith said fixed contact and subsequently into engagement with saidsecond contact upon predetermined expansion of said element and beingsubsequently operable to automatically actuate said contact means out ofengagement with said second contact and subsequently back intoengagement with said fixed contact upon a subsequent predeterminedcontraction of said element, and abutment means carried on said secondlever engageable with said fixed lever upon further expansion of saidelement to pivot said fixed lever relative to said second lever andactuate said second contact out of engagement with said contact means.

4. A thermostatic control device comprising a casing, a pair of pivotallevers mounted in said casing, a pair of mating contacts, one of saidcontacts being mounted on each of said levers, means for biasing one ofsaid levers to a predetermined position, and means responsive to atemperature condition including an expansible element mounted on saidcasing and engageable with the other of said levers to actuate the sameto close said contacts in response to a predetermined expansion of saidelement and to rotate said one lever against said bias from saidposition upon further expansion of said element.

5. A thermostatic control device as claimed in claim 4 wherein a thirdfixed contact is mounted on said casing in spaced relation to saidcontact carried by said one lever, and said contact carried by saidother lever is moved out of engagement with said third contact and intoengagement with said contact of said one lever upon said predeterminedexpansion of said element.

6. A thermostatic control device as claimed in claim 5 wherein saidother lever is provided with an abutment adjacent one end thereof forengagement with said one lever during said further expansion of saidelement to effect disengagement of said pair of contacts.

7. A thermostatic control device comprising a casing, a pair of pivotallevers mounted in said casing, a pair of mating contacts, one of saidcontacts being mounted on each of said levers, means for biasing one ofsaid levers to a predetermined position, means responsive to atemperature condition including an expansible element mounted on saidcasing and engaging the other of said levers to actuate the same toclose said contacts in response to a predetermined expansion of saidelement and to rotate said one lever against said bias upon furtherexpansion of said element, and a second pair of contacts within saidcasing, one of said second pair being fixed to said casing and the otherof said second pair being carried by said one lever in engagement withsaid fixed contact in said predetermined position of said one lever,said one contact of said second pair being moved out of engagement withsaid fixed contact by said further expansion of said element.

References Cited in the file of this patent UNITED STAT ES' PATENTS2,385,434 Weber Sept. 25, 1945 2,403,824 Newell July 9, 1946 2,441,192Graves May 11, 1948 2,591,803 Garner Apr. 8, 1952 2,671,136 G-reenawaltMar. 2, 1954 2,715,664 Garner et al. Aug. 16, 1955 2,718,574 Weber et alSept. 20, 1955

